Rare insults

Interestingly, English does have a "reference" accent. "Queens English".

Back in the days of the British empire, the aristocracy had a serious problem. When they traveled, the local population were difficult to understand, they all had accents. To solve this, the hired help were taught not just English but a clear "accentless" English. This meant the rich could go anywhere in the empire and not have to decode the local's butchering of English.

While it's used a lot less now, it was only a few decades back that the BBC stopped requiring it for news broadcasts. It's the "classic" British accent you see on TV shows.